src/ec: Use 'include <stdlib.h>' when appropriate

Change-Id: Ifdb2dee08da45d698174583ee5ed44bf5a0243ff
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32823
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/ec/kontron/it8516e/ec.c

@@ -13,7 +13,6 @@
  * GNU General Public License for more details.
  */
 
-#include <stdlib.h>
 #include <console/console.h>
 #include <device/device.h>
 #include <device/pnp.h>